Electric machines i.e. electric motors and electric generators are used in many applications. Electric motors are used to drive different kinds of machines and electric generators are used to produce electric power. The power sources used to drive electric generators vary. Steam is one common power source used in electric power plants to drive turbines, whereby the turbines drive the electric generators. Combustion engines can on the other hand be used to drive generators. The combustion engine and the generator are often mounted on a common platform forming a support structure. The whole unit comprising the combustion engine and the electric generator on the common support structure can then be transported to the site and positioned on the floor in the power building. The installation of such a unit is thus very fast.
The stator in an electric generator comprises normally an annular stator core and a stator frame surrounding the stator core. The inner surface of the stator core comprises slots opening into the inner surface of the annular stator core. The stator winding is positioned in the slots. There are further back beams extending in the axial direction along the outer surface of the stator core. The back beams are welded to the outer surface of the stator core. The stator frame comprises normally end constructions and frame plates between the end constructions. The stator frame can be manufactured simultaneously with the stator core. The stator frame can then be installed on the stator core when the stator core is ready.
The stator frame is in prior art solutions attached via support elements to the support structure. The support elements are attached by welding to the stator frame and to the support structure by bolts.
The stator core is in prior art solutions also attached to the stator frame by welding. This is done e.g. by using C-formed clamps that are positioned on the back beams on the outer surface of the stator core. The C-clamps are then welded to the stator frame and to the back beams on the stator core. The stator core is first positioned in the correct position in relation to the stator frame before the welding is done.
The use of welding for attaching the stator core to the stator frame and for attaching the support elements to the stator frame is, however, problematic especially in generator applications where the generator is driven by a combustion engine. The combustion engine produces heavy vibrates to the common support structure and thereby also to the electric generator. The electric generator will thus work in a constantly vibrating environment. These vibrations will cause a heavy load on the welded joints during the long lifespan of the generator. The number of vibrations that an electric machine is subjected to during its lifetime is in the order of 109. The great number of vibrations is problematic for welded joints, which might at some point brake due to these vibrations. It has in fact been observed that these vibrations have caused braking of the welded joints in some circumstances. The welded joints between the stator frame and the support elements are weak points in the construction as the moment of inertia of the stator is transferred from the stator to the support structure through these joints.
There is thus a need to find a solution to the problem of welded joints that might brake due to vibrations.
U.S. Pat. No. 4,207,484 discloses an electric machine comprising a rotor and a stator surrounding the rotor. The stator laminations are compressed between two opposing press rings which are secured by a plurality of draw bolts that are threaded and provided with nuts. The stator rests on two axially orientated stator support members. The support members include a horizontal supporting plate that supports a sole that is affixed to the upper radial projections of the press rings. More particularly each sole is connected in a force-transmitting manner to the stator core by a number of supports that may be welded or otherwise affixed between the sole and adjacent draw bolts of the stator core. Each sole is attached to its corresponding supporting plate by a plurality of bolts that are screwed to the supporting plate. Thus a rigid supporting connection is provided between the support members and the stator core.
U.S. Pat. No. 102,406 discloses an electric machine comprising a rotor and a stator surrounding the rotor. The stator is supported with support feets made of cast iron on a support structure.
U.S. Pat. No. 1,689,503 discloses an electric machine comprising a rotor, a stator surrounding the rotor and a support structure. The stator is construed in four parts i.e. an annular structure, foot members, and a cover structure which is made in two parts secured together. The annular structure comprises a plurality of axially space apart annular members extending around the whole perimeter of the cylindrical stator core. The annular members are connected by axially on the inner perimeter of the annular members extending first tie bars and by axially extending on the outer perimeter of the annular members extending second tie bars. The first axially extending tie bars are attached to the outer perimeter of the stator core. Each foot member comprises a plurality of curved plates spaced apart which are secured, preferably by welding, to a base plate and a side plate. The curved plates extend only over a certain angle along the perimeter of the annular structure. The curved plates are bolted to the annular members. The cover structure comprises two parts secured together with bolts. The cross section of the cover structure has a curved form so that it can be fitted as a cover on the annular structure and the foot member.